1. Field of the Invention
The present invention relates to a piston type compressor, in which fluid is compressed by means of reciprocating pistons connected to a swash plate. More particularly, it relates to a guiding mechanism for reciprocating pistons, which improves the slidability of the pistons in the compressor.
2. Description of the Related Art
Swash plate type compressors have a wide variety of applications including the use in an air conditioning system for automobile and/or a refrigerating system. Among those compressors, a single head piston type compressor is widely known, which compresses fluid by means of reciprocating pistons connected to a swash plate. A conventional single head piston type compressor is disclosed in the U.S. Pat. No. 4,664,604.
As shown in FIG. 6, a cylinder block 41 is accommodated in a cylindrical housing 40 of a compressor. Pistons 42 are accommodated in cylinder bores 41a and reciprocally movable therein, respectively. A drive shaft 44 is rotatably supported by means of the central portion of the cylinder block 41 and the front cover 43. The drive shaft is driven by an engine. A drive plate 45 is mounted on the drive shaft 44, and synchronously rotates with the shaft 44. Further, a swash plate 47 is tiltably mounted on the shaft 44, and is reciprocally slidable together with a spherical sleeve 46 along the axis direction of the shaft 44. The drive plate 45 and the swash plate 47 are connected, by means of a hinge mechanism 48. The circumference of the swash plate 47 is engaged with the proximal portion of the associate piston 42.
According to the above-described compressor, when the shaft 44 is rotated, the drive plate 45 is rotated together with the shaft. The rotation of the plate 45 is transferred to the swash plate 47 through the hinge mechanism 48. The plate 47 is rotated with the surface inclined with respect to the shaft, so that the pistons 42 reciprocate in the cylinder bores 41a, respectively. Therefore, the refrigerant gas sucked into an inlet chamber 52 is compressed, and discharged into an associate discharge chamber 53, respectively.
Control of the displacement of the compressor can be achieved by varying the stroke of the piston. The stroke of piston varies depending on the difference between pressures which are acting on both sides of the swash plate 47, respectively. The difference is generated by balancing the pressures between the pressure in a crank chamber 50 acting on the rear surface of the piston 42 and suction pressure in the cylinder bore 41a acting on the front surface of the piston 42, and acts on the swash plate 47, through the piston 42.
According to the conventional compressor, each one of the pistons 42 has a cylindrical shape. Further, connecting portions 51 for engaging shoes 49 are formed at the proximal portion of the pistons 42, respectively. The diameter or radius of curvature of the connecting portion 51 is substantially equal to that of the piston 42. Therefore, a gap hardly exists between the circumference of the connecting portion 51 and the inner wall of the housing 40. Even when the pistons 42 reciprocate, it is difficult to lead the refrigerant gas containing lubricant oil that is in the crank chamber 50 from the periphery of the connecting portion 51 to the slide portion of the cylinder bore which corresponds to the piston. The lack of lubrication at the slide portion will result in rapid wear, so that durability is lowered.